Reaction of [Cp∗2W2O5] with mercaptocarboxylic acids: Addition rather than reduction. Isolation and characterization of Cp∗WO2(SCH2CH2COOH)

The reaction of Cp∗2W2O5 with HS(CH2)nCOOH (n = 1, 2) in MeOH or in CH2Cl2 solutions at room temperature proceeds in slightly different ways depending on the value of n. For n = 2, it selectively yields compound Cp∗WO2(SCH2CH2CO2H), which has been isolated and characterized by elemental analysis, NMR and single crystal X-ray diffraction. The reaction is equilibrated, being shifted to the product by absorption of water by anhydrous Na2SO4 in CH2Cl2, and to the reactants by addition of water. Contrary to the Mo analogue, no products resulting from metal reduction are obtained. The corresponding reaction for n = 1 occurs similarly at low substrate/W ratios (<0.5), but proceeds further to several uncharacterized products for greater substrate amounts. The primary product could not be isolated, but its 1H NMR spectrum suggests a different, asymmetric structure.